This invention relates to the use of asynchronous transfer mode (ATM) facilities for the transfer of synchronous transfer mode (STM) bearer traffic and, in particular, to the use of cached switched virtual circuits (SVCs) to facilitate connection setup through the ATM network.
Introduction of the Internet to the general public and the ensuing explosion of interest and demand for access to the Internet through telephone service provider networks has placed considerable strain on existing telecommunications facilities. In addition, telephone service provider networks are now being overwhelmed by the explosion of data traffic over an infrastructure that was not intended for and is not capable of supporting the exponential increase in demand currently being experienced.
Consequently, a keen interest has developed among telephone service providers for increasing network capacity by off-loading at least a portion of the calls handled to an alternate bearer traffic transport. Currently, asynchronous transfer mode (ATM) networks are considered to be the most likely candidate for service as an alternate bearer traffic network. ATM networks have the flexibility to efficiently transfer both voice and data between time division multiplex (TDM) switches.
Although ATM networks possess the required flexibility to handle the current bearer traffic mix in the public switched telephone network (PSTN), the ATM network is not well suited to provide call connection services at the speed to which PSTN subscribers have become accustomed. The establishment of a virtual connection across an ATM network may introduce unacceptable delays in call setup, depending on the number of ATM nodes involved in the SVC and the call setup request rate. Consequently, before a significant volume of traffic can be transferred to an ATM backbone, some method of facilitating call setup is required if customer satisfaction is to be ensured. One method of ensuring rapid call completion is to utilize permanent virtual circuits (PVCS) or permanent virtual paths (PVPs) in the ATM network to facilitate call setup. Since the PVCs and PVPs are preconfigured, call setup rates easily meet customer expectations. There is a significant drawback to using PVCs or PVPs for bearer traffic transfer through an ATM network, however. The PVCs and PVPs, much like PSTN voice trunks, consume resources regardless of their occupancy. The PVCs and PVPs are also laborious to maintain and the operations and maintenance requirement contributes to overhead.
Consequently, it is accepted that SVCs are preferred for the transfer of bearer traffic through an ATM network. A network Working Group Internet-draft document published on the Internet in October, 1997 proposes a rudimentary ATM SVC caching method in which virtual circuits are cached in pools of unspecified bit rate connections for transferring IP packets over an ATM backbone network. The paper does not explain how the cached SVCs are established or maintained. A problem with the proposal in the draft document is that it does not describe any dynamic method for managing cached SVCs to balance bandwidth usage and switch resource usage to ensure efficient use of resources. A method and apparatus for caching SVCs to rapidly establish a communication connection through an ATM network was also described in applicants"" copending U.S. patent application Ser. No. 09/053,682 filed Apr. 2, 1998. In accordance with that method, the SVCs were established and controlled within the ATM network. While the method is both efficient and effective, it requires minimal functionality in the ATM network which may not be universally available. Consequently, it is desirable to provide a method and apparatus for reduction of call setup rate in an ATM network which is entirely ATM network-independent to permit the method and apparatus to be universally applied for the transfer of switched telephone network bearer traffic over an ATM backbone network.
It is an primary object of the invention to provide a network-independent method and apparatus for reduction of call setup rate in an ATM network.
It is a further object of the invention to provide a method and apparatus whereby SVC setup and control is effected in edge device interfaces to the ATM network.
It is yet another object of the invention to provide a method and apparatus for centrally controlling the edge device interfaces to exercise control of an SVC caching policy at a central operations and management facility.
It is yet a further object of the invention to provide a method and apparatus in which cached SVCs are organized in a plurality of cache pools, a cache pool existing between a first and second edge device with which the SVCs are established.
It is a further object of the invention to provide a method and apparatus in which the caching policy manager executes an algorithm to determine the number of cached SVCs that are to be included in each cached SVC pool.
It is yet a further object of the invention to provide an apparatus and method in which each pool of cached SVCs is managed by a separate instance of a caching manager.
It is yet another object of the invention to provide a method and apparatus in which each cache pool has a master caching manager located at a first end of the pool and a slave caching manager located at an opposite end of the cache pool.
These and other objects of the invention are realized in a method for reducing call setup rate in an asynchronous transfer mode (ATM) network where edge devices serve as interfaces for ingress and egress of bearer traffic from other networks, comprising:
maintaining at each edge device a pool of cached switched virtual circuits (SVCs) for the transfer of bearer traffic through the ATM network, and dynamically adjusting the number of cached SVCs in the pool of cached SVCs by adding SVCs to the pool when bandwidth usage is low with respect to switching resource usage, and removing SVCs form the pool when bandwidth usage is high with respect to switch resource usage.
The invention also provides a method for reducing call setup rate in an asynchronous transfer mode (ATM) network where edge devices serve as interfaces for ingress and egress of bearer traffic from other networks, comprising:
maintaining at each edge device a plurality of pools of cached switched virtual circuits (SVCs) for the transfer of bearer traffic through the ATM network, the plurality of pools at a first edge device respectively containing cached SVCs for connections between the first edge device and second edge devices that respectively serve as interfaces for the ingress and egress of the bearer traffic; and
when a bearer traffic connection is passed to one of the first or second edge devices, one of the cached SVCs in an appropriate pool is selected to serve the call if a cached SVC exists in the appropriate pool.
In accordance with a further aspect of the invention there is provided an apparatus for reducing call setup rate in an asynchronous transfer mode (ATM) network where edge devices serve as interfaces for ingress and egress of bearer traffic from other networks, comprising:
a caching manager active on each edge device for managing a pool of cached SVCs between the edge device and other edge devices in the network; and
a caching policy manager for providing the caching managers with caching policy to determine a maximum cache size for each pool of cached SVCs in the ATM network.
The method and apparatus in accordance with the invention provide a network-independent control of switched virtual circuits to reduce call setup rate in an ATM network by establishing and maintaining pools of SVCs through the ATM network. Each pool of SVCs is preferably managed from each edge device interface by a separate instance of a caching manager which receives operational parameters from a centralized caching policy manager. The caching policy manager is preferably adapted to designate a master and a slave caching manager for each pool. The behaviour of the caching manager being dependent on its designation as master or slave.
Each cache pool is preferably a dynamic cache. A dynamic cache consists of one or more SVCs established between two end points that are available and idle. In addition to the dynamic cache, a number of active connections may also exist between the same end points. An active connection that becomes idle may be returned to the cache, and reused in any subsequent call setup.
Since SVC caching is effected in the edge device interfaces, the method and apparatus in accordance with the invention are network-independent and adapted for use with any ATM network. The edge device interfaces in accordance with the invention are preferably equipped to interface with TDM switches in telephone service provider networks. In a preferred embodiment of the invention, the interfaces may be connected by a single large trunk group to the TDM switches in order to minimize trunk management overhead. While this arrangement facilitates management of the TDM switch, it potentially contributes to cache fragmentation if the TDM switch requires more than one edge device interface to serve traffic load. The invention therefore further provides methods and apparatus for reducing cache fragmentation by consolidating edge device interfaces into a single large logical edge device interface. Alternatively, multiple trunk groups respectively dedicated to a predetermined subset of the bearer traffic may be used for the same purpose.